Calibration of an interferometer

Abstract

In a method for calibrating an interferometer (100) having a beam path for a measuring beam (112), wherein at least one plane (320) that at least partially reflects the measuring beam (112) has been introduced into the beam path, and wherein a normal to a first plane (320) is inclined at a first angle to a measuring beam (112) incident on the first plane (320), the following steps are carried out: interferometric measurement of a first axial spacing of a first point on the first plane (320) with the measuring beam (112), and interferometric measurement of a second axial spacing of a second point on one of the at least one plane (320) with the measuring beam (112), wherein the second point is spaced apart from the first point.

The invention claimed is: 
     
       1. A method for calibrating an interferometer having a beam path for a measuring beam, wherein at least one plane that at least partially reflects the measuring beam has been introduced into the beam path, and wherein a normal to a first plane is inclined at a first angle to a measuring beam incident on the first plane and wherein the following steps are carried out:
 a. interferometric measurement of a first axial spacing of a first point on the first plane with the measuring beam; 
 b. interferometric measurement of a second axial spacing of a second point on one of the at least one plane with the measuring beam, wherein the second point is spaced apart from the first point. 
 
     
     
       2. The method according to  claim 1 , wherein the first plane has a planarity which is below the measurement accuracy of the interferometer. 
     
     
       3. The method according to  claim 1 , wherein a measuring lens is positioned from a first position, for measuring an object in the measuring position, to a second position for calibrating the interferometer, such that the measuring lens is directed at the first plane. 
     
     
       4. The method according to  claim 1 , wherein, in order to measure the second axial spacing, the measuring beam is displaced laterally by a first distance on one of the at least one planes such that the second point is spaced apart from the first point. 
     
     
       5. The method according to  claim 4 , wherein the measuring beam is guided to an optics by a tilting mirror, wherein, as a result of the tilting mirror being inclined, the measuring beam emerging from the optics is laterally displaced by the first distance on one of the planes. 
     
     
       6. The method according to  claim 4  or  5 , wherein, by the first angle and a difference between the first axial spacing of the first point and the second axial spacing of the second point, the first distance between the first point and the second point is calculated. 
     
     
       7. The method according to  claim 6 , wherein the first axial spacing of the first point and the second axial spacing of the second point on the first plane inclined at the first angle are measured, and wherein an axial spacing of a third and an axial spacing of a fourth point are measured on one of the planes, which is or has been tilted at a negative value of the first angle, wherein all of the points are spaced apart from one another in pairs. 
     
     
       8. The method according to  claim 6 , wherein the first plane is inclined at the first angle about a first axis, wherein a second plane for measuring the distances of the third and of the fourth point is inclined at a second angle about a second axis that is not parallel to the first axis. 
     
     
       9. The method according to  claim 1 , wherein the first point and the second point are each points of a single, common trajectory, and wherein a plurality of points of the trajectory are measured and wherein the trajectory has a minimum radius of curvature which amounts to at least 1/7 of a radius of a circumference of a surface to be measured.